Well treating method



United States Patent 3,199,585 WELL TREATTYG METHGD Luther C. Cronberger, Sanford, Micln, assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Filed Mar. 13, 1963, Ser. No. 264,827 13 Claims. (Cl. 166-1) This invention relates to the treating of cased well bores and particularly to a method of depositing a protective coating on the well casing.

Tubular goods, such as casing, for example, disposed in an earth well are often subject to electrolytic microbic or chemical corrosion, or a combination of these.

In many locations corrosion of the external surface of the casing due to action on the casing by corrosive fluids from adjacent earth formations results in casing leaks within a year, or even less, after the pipe is set.

Repair of such leaks is often very costly. Cathodic protection techniques have been used to reduce such corrosion, and are helpful to a degree. However, when the corrosion is of a chemical rather than an electrolytic nature, as is often the case, cathodic protection is unsatisfactory.

Pipe lines have long been protected against corrosion by using lined pipe in combination with cathodic protection.

The use of externally coated pipe wherein the coating is applied above ground has been tried, but with limited success. The coating scrapes off in spots as the casing is run. Coating of the couplings between lengths of casing must be done on the rig floor as the casing is run, and the coating thus provided on the couplings usually is too thin to stand up under bole-hole conditions. Accordingly, a principal object of this invention is to provide an improved method of achieving anti-corrosion protection of easing surfaces under bore-hole conditions.

Another object of this invention is to provide an improved method of depositing a protective coating on a surface of a tubular member disposed in the bore of an earth well.

In accordance with this invention an electroplatable dispersion or solution, in which the substance to be plated out or deposited is an electrical insulator, is pumped or otherwise disposed between the casing and the bore hole wall. A direct electrical current is then applied between the casing and a remote grounded electrode. The material is deposited on the casing, building up a thickness of insulating coating of 100 mils or more, depending on the time the current is applied and other conditions under which the treatment is made.

The thus deposited coating, of a latex, for example, is more or less fluid impervious and electrically insulating in nature. For wells where corrosion conditions are quite bad, cathodic protection means, such as magnesium anodes, are usually recommended if only on the theory that their additional insurance against corrosion is not prohibitive in cost.

The invention, as well as additional objects and advantages thereof, will best be understood when the following detailed description is read in connection with the accompanying drawing. The single figure shows, in diagrammatical form, an earth well and apparatus used in practicing this invention.

Referring to the drawing there is shown a bore hole, indicated generally by the numeral 10, which extends from the surface 12 of the earth through a number of earth formations and into a so-called pay zone 14 containing oil, gas, water or other recoverable material. Alternatively, the pay zone 14 may be the input zone of a water flooding injection well or the like.

. mixer 38, and well pressurizing pump 40 3,199,585 Patented Aug 10, 1955 The bore hole 10 has so-called surface pipe 16 which is bonded to the adjacent wall 18 by the cement 20.

A string of casing 22, suitably centralized in the bore hole, extends from the surface of the earth into or through the pay zone 14 and has a suitable casing head 24 at its upper or surface end.

In making one treatment in accordance with this invention equipment at the well site included a reservoir of the dispersion, emulsion or solution 26, an additives reservoir 28, a drilling mud reservoir 36, a cement reservoir 32, and a water reservoir 34. A booster pump 36, are also provided. v i

The reservoirs 26, 28, 30, 32, 34 are each coupled to a header line 42 through valves 44, 46, 48, 50, 52 respectively. The header 42 is coupled to the booster pump 36 and then through the valve 54and line 56 to the pressu-rizing or treating pump 46. Alternatively, with the valve 54 closed, the output of the booster pump 36 may be coupled to the pump 40 through the valve 58, line 60, mixer 38 and valve 62.

A valve 64 is in the line 66 between the casing head 24 and the pump 40. a

A direct current generator 68 has one terminal coupled through an 'ammeter 70 to a suitable remote ground connection 72 which may be the casing of a nearby well, a driven metal ground electrode or any other suitable means which provides low resistance contact with the earth. The other terminal of the generator 68 is electrically coupled, through the switch 74 and line 76, to the casing as at the casing head 24, for example. A voltmeter 78 is connected across the output circuit of the generator 68.

Well bore survey apparatus 86, of a type adapted to measure the potential, either naturally existing or impressed, along the casing 22 is indicated diagrammatically as being coupled to the casing at the casing head 24. Since such survey equipment is not used in practicing the method of this invention but in confirming the successful practicing of the invention, no structure of the survey apparatus 80 is shown. A micropotential profile, a type of survey well known to those who are skilled in the well surveying art, is, for example, suitable for use in connection with this invention.

In making treatments in accordance with this invention itis often desirable to flush out the annular space between the casing 22 and the well bore wall with water or other suitable material to clean drilling mud, cement, or weighting material from this space. Experience has shown that some of the emulsions or solutions used in the treatment are not compatible with the above mentioned materials, and when such emulsions or solutions are used the cleanout step is essential if not already done before the treatment is begun.

An amount of dispersion or solution which is at least equal in volume to the amount required to fill the part of the annular space along which the casing is to be coated is pumped down the casing. In the drawing, this is the space occupied by the emulsion 82, or from near the top of the shale strata to the surface of the earth.

As shown in the drawing, the entire annular space along the casing from the lower end of that part of the casing which is to be treated and the bottom of the casing is not filled with cement. A slug of filler of suitable density (more dense than the above mentioned dispersion or solution to prevent settling through the filler) such as a weighted drilling mud is pumped down the casing in an amount sufiicient to fill the annular space 84 along the casing between the lower end of the part of the casing to be treated andthe top of the annular space 86 along the casing which is to be filled with cement.

Following the weighted filler material, cement is pumped a down the casing in an amount suflicient to fill the space between the bottom of the bore hole and the bottom of the space occupied by the tiller.

In practice, a plug 86 is inserted in the casing on top of the cement and the suspension, filler material and the cement are pumped down the casing and forced up the annular space between the well casing and the well bore wall.

If need be, the plug and cement remaining in the easing may be drilled out later.

A direct electrical current is then applied across the casing 22 and the remote electrode 72 by closing the switch 74. The polarity applied across the casing and the remote electrode or electrodes depends on whether the emulsion or solution 82 to be deposited on the casing is cationic or anionic.

If the dispersion or solution is anionic the casing or surface onto which the deposit is to be made is made electrically positive with respect to the remote electrode. Conversely, for cationic dispersions or solutions the easing or surface is made electrically negative with respect to ground.

A suitable ground may be the casing of an adjacent well or a number of drilled holes each having 60 to 80 feet of tubing disposed therein, the holes preferably being filled with an electrolyte. A terminal of the generator 68 is connected to the casing of the ground well or connected in parallel with the tubing in the drilled holes. Preferably the grounded electrode or electrodes are disposed a hundred feet or more from the casing or surface being treated.

The practical limitation on spacing between the treated well and the ground electrodes or electrode is the resistance involved in the cables connecting the electrodes. That is, excessive cable length results in enough voltage drop to offset the advantage of somewhat better current distribution along the casing which occurs when the ground or back electrode is widely spaced from the easing.

The amount of electric current applied between the two electrodes and the time during which it is applied vary with the amount of surface to be coated, the type of material being deposited, the nature of earth fluids Which enter the annulus between the bore hole and the casing (brine, fresh water, etc.), and the number and location of the so-called back electrodes, for example.

It has been found, in practice, that for coating 4,000 feet of 7 inch casing or 5,200 feet of inch casing, current of from 500 to 1000 amperes applied to the casing for a period of 30 minutes results in a good coating being deposited on the outer surface of the casing.

Although the conditions in the earth strata along the well bore may be such that non-uniform current flow to the adjacent casing occurs, the more rapid deposition of the protective film or coating on the part of the casing having heavier current flow rapidly builds up a coating resistance which tends to divert current flow to other parts of the casing.

Average current flow of about ma./sq. ft. to 20-0 ma./sq. ft. applied to the casing for a period of time equal to from 36 to 360 ampere seconds/sq. ft. has proven satisfactory to form adequate coatings on the casing, although higher rates of current flow may be used.

In theory the current should decrease and approach a constant value at constant voltage as the coating process is completed, but often such conditions do not occur in actual practice because the current finds other paths to follow through the earth to the casing, thus changing the resistance encountered and with it the amount of current flow.

The particular dispersion or emulsion used in the above described treatment (to fill the space 82) is a cationic asphalt dispersion whose batch composition is composed of 34 pounds of 200-250 penetration grade asphalt, 72 grams of N-3-aminopropyloctadecylamine, 19% pounds of water, 23.5 grams of calcium chloride and 61 cubic centimeters of 35 percent strength hydrochloric acid.

The first two ingredients are pre-mixecl at about 220 F. and the last three ingredients are pre-mixed at about 180 F.

The pro-mixed asphalt containing ingredients are added to the water containing pre-mixed ingredients with shear agitation at a temperature of to F.

The batch recipe is scaled upwardly or downwardly, as needed, to provide the volume amount of dispersion required for a particular treatment.

Dispersions of other materials which may be used as substitutes for the above described asphalt containing dispersion include film-forming latexes of interpolymeric materials. Such latexes are well known items of commerce or may be tailor made for special formulations using known emulsion polymerization technology. Typical latexes operable as the aforementioned substitutes in the present inventive concept include those of copolymers of from about 0 to 80 percent by weight of at least one monoalkenyl aliphatic monomer together with at least one ethylenically unsaturated comonomer such as an alkyl acrylate or methacrylate, an aryl acrylate or methacrylate, acrylic or methacrylic acid or an open chain aliphatic conjugated diolefin of about 4 to 9 carbon atoms. Other latexes such as those of butadiene and acrylonitrile; of vinylidene chloride and acrylonitrile; of vinylidene chlo ride and vinylacetate; of vinylchloride and vinylacetate will be well known to the worker in the art. In addition terpolymers and quaterpolymers of such monomers may be used with effectiveness.

Blends and mixtures of two or more of the above described latexes or equivalents may be used with efficacy within the concept of the invention. Likewise contemplated are the pumpable dispersions of graft copolymers and similar polymeric entities.

Typically, such latexes contain from about 25 to 60 percent polymer solids and that range of polymer solids is preferred for use in the present concept. Lower solids may be employed although such latexes involve the transfer of large volumes of liquid relative to the coating thickness obtained therefrom.

The inventive concept involves the electrodeposition of the latex solids on the well casing. Consequently it is requisite that the individual particles of the latex be electrically charged. With non-polar polymeric materials such as styrene, butadiene copolymers the charge is obtained by the use of ionic emulsifying agents in the preparation of the latex. Anionic emulsifiers which may be used include alkali metal alkyl sulfates or sulfonates, the alkyl aryl sulfonates and soaps from sodium or potassium hydroxide, oleic acid, stearic acid, palmitic acid, capric acid, tallow fatty acid. Cationic emulsifiers, such .as the reaction products of fatty acids with various ethyleneamines, may likewise be employed. It should be apparent that the nature of the charge on the latex particle will dietate the direction of migration of that particle. It has been found that small amounts of nonionic surfactants which are commonly added to polymer latexes to impart mechanical stability thereto may be used in the present concept without adversely affecting the rate or direction of migration of the polymer particles. Latexes which contain polar groups such as the carboxylate group may migrate under electrical inducement without requiring an ionic emulsifier.

While it is not practical in most cases to directly determine if a satisfactory coating has been formed on the casing after the current has been applied in accordance with this invention, such determination may be made indirectly. For example, if the dispersion or solution to be deposited is circulated up the annulus followed by drilling mud, the drilling mud may, after the coating has been deposited, be circulated out of the annulus. If the material fiowing out of the annulus at the surface shows none of the solids of the film or coating forming material, it is reasonable to assume that all the material was in fact deposited on the casing in the form of a coating and that the coating is rather adherent in nature.

The extent of effectiveness may be shown, too, by running a micropotential profile before and after the coating is deposited and noting the effect of the coating resistivity along the casing on the potential measured in making the survey.

The invention has thus far been described in connection with the type of situation where the material to be deposited as a film or coating on the outer wall of the casing 22 is pumped up the annulus between the casing and well bore wall ahead of drilling mud and/or cement slurry.

It is also practicable in the treatment of previously completed wells where the casing is subject to considerable corrosion, to perforate the casing above the cemented part and inject the dispersion or solution to be deposited through the perforation. Squeeze cement techniques are then used to effectively close the perforations in the casing. The actual depositing of the coating or film on the casing is accomplished by applying appropriately polarized electric current as discussed previously herein.

It is also practicable in many instances to deposit a slug of solution or dispersion in the annulus, between the casing and bore hole well, apply electric current between the casing and the remote electrode or electrodes, and slowly pump additional material down the casing to force the slug of solution or dispersion past the part of the surface of the coating on which the protective coating or film is to be deposited. The rate of movement of the slug along the casing should be determined in accordance with the result of the consideration of the type of solution or dispersion and the current density applied to the casing to insure adequate time for depositing the coating or film on the outer surface of the casing.

A possible disadvantage to the slug method of depositing a coating or film on the casing is the amount of depositable material which is contained in a slug, thus limiting the length of casing which can be coated with each socalled slug of material. Also, since the conductivity of the adjacent earth formations vary, a coating of nonuniform thickness are measured along the casing may be deposited.

Although such situations may be rare, it is also practicable to simply pour down the casing-well bore annulus the solution or dispersion to be deposited and then apply direct current of the required polarity to the casing and the remote electrode.

It should be emphasized that not all coatings deposited on the casing will act as good electrical insulators because conductive particles present in the annulus may be carried into the coating or gas liberated as the coating is deposited may, under some conditions, result in a porous coating. However, a judicious selection of dispersion, deposition rate, and cleaning techniques to remove unwanted material from the annulus will minimize the problem of conductivity through the coating. The use of cathodic protection techniques, as mentioned before, is a valuable supplement to this method of protecting casing against corrosion.

While 20 ma./sq. ft. to 200 ma./sq. ft. form adequate coatings on the casing, initial currents as high as amperes per square foot have been used in tests. This high current rapidly decreases, usually within two or three minutes, to a current of a few milliamperes per square foot as the coating builds up and forms a resistance to the passage of current between the casing and the remote electrode.

It is also believed that the deposited coating provides additional protection against corrosion by serving as an oxygen free, high pH barrier against bacterial attack.

While asphalt and latex dispersions have principally been described in connection with this invention, coal tar emulsions or dispersions may also be used.

What is claimed is:

1. A method of depoisting a protective coating on the outer surface of a tubular member disposed in the bore of an earth Well comprising connecting said tubular member to a source of electrical potential such that said tubular member constitutes a first electrode, connecting a second electrode spaced from said tubular member and contacting the earth to said source of electrical potential, disposing an electro-platable dispersion containing solids between said outer surface and said well bore and then applying an electric current of predetermined polarization between said first electrode and said second electrode whereby current passes through said dispersion to deposit solids from said dispersion onto said surface, the polarization of the charge on said tubular member being opposite that of solids in said dispersion.

2. A method in accordance with claim 1, wherein said current is between 10 amperes and 2 milliamperes per square foot of surface to be coated.

3. A method in accordance with claim 1, wherein said dispersion is a film forming latex of inter polymeric materials.

4. A method in accordance with claim 1, wherein said dispersion is an asphalt base dispersion.

5. A method in accordance with claim 1, wherein the applied current is between 200 milliamperes and 20 milliamperes per square foot of surface to be coated.

6. A method in accordance with claim 1, wherein the space between said outer surface and said bore hole is flushed with water before disposing said dispersion therein.

7. A method in accordance with claim 1, wherein current is applied to the earth through at least one electrode which is remote from said bore hole.

8. A method in accordance with claim 1, wherein said surface to be coated is the positive electrode when an anionic dispersion is used.

9. A method in accordance with claim 1, wherein said surface to be coated is the negative electrode when a cationic dispersion is used.

10. A method in accordance with claim 1, wherein said dispersion contains between 25 and 60 percent solids.

11. A method in accordance with claim 1, wherein said dispersion comprises copolymers of from about zero to percent by weight of at least one monoalkenyl aliphatic monomer together with at least one ethylenically unsaturated comonomer.

12. A method in accordance with claim 1, wherein said dispersion is disposed between said surface and said bore hole by pumping the dispersion down said tubular member and then displacing it upwardly along the annulus between said surface and said bore hole.

13. A method in accordance with claim 1, wherein said dispersion provides an electrolytic path between said surface and the earth.

References Cited by the Examiner UNITED STATES PATENTS 1,890,476 12/32 Willigen 204-182 2,217,857 10/40 Byck 16621 2,426,317 8/47 Menaul 166--1 FOREIGN PATENTS 7/58 Great Britain.

OTHER REFERENCES CHARLES E. OCONNELL, Primary Examiner.

BENJAMIN HERSH, Examiner. 

1. A METHOD OF DEPOSITING A PROTECTIVE COATING ON THE OUTER SURFACE OF A TUBULAR MEMBER DISPOSED IN THE BORE OF AN EARTH WELL COMPRISING CONNECTING SAID TUBULAR MEMBER TO A SOURCE OF ELECTRICAL POTENTIAL SUCH THAT SAID TUBULAR MEMBER CONSTITUTES A FIRST ELECTRODE, CONNECTING A SECOND ELECTRODE SPACED FROM SAID TUBULAR MEMBER AND CONTACTING THE EARTH TO SAID SOURCE OF ELECTRICAL POTENTIAL, DISPOSING AN ELECTRO-PLATABLE DISPERSION CONTAINING SOLIDS BETWEEN SAID OUTER SURFACE AND SAID WELL BORE AND THEN APPLYING AN ELECTRIC CURRENT OF PREDETERMINED POLARIZATION BETWEEN SAID FIRST ELECTRODE AND SAID SECOND ELECTRODE WHEREBY CURRENT PASSES THROUGH SAID DISPERSION TO DEPOSIT SOLIDS FROM SAID DISPERSION ONTO SAID SURFACE, THE POLARIZATION OF THE CHARGE ON SAID TUBULAR MEMBER BEING OPPOSITE THAT OF SOLIDS IN SAID DISPERSION. 